The invention relates to an electric servo-steering arrangement for motor vehicles with a rotational angle sensor configuration as well as to a method as well as to a method therefore.
The invention addresses a steering arrangement for motor vehicles with power-assisted drive, in which via a rotational angle sensor a desired steering movement is detected, via regulation devices a theoretical-actual deviation is determined, thereupon a required adjustment moment is calculated and the appropriate power is supplied to the power-assisted drive.
Various steering arrangements of this type are known in prior art. In particular, in recent times there are increasingly found steering arrangements with electric power-assisted drive (DE 10141199A1) or, circumventing the mechanical coupling between steering wheel and wheels, with direct electric drive of the steering adjustment of the wheels.
For measuring the angle in prior art, Hall sensors are frequently employed. Therein onto the rotatable part magnetic elements are fastened, whose polarity changes in a fixed time pattern. A Hall probe correspondingly picks up the Hall voltage caused by the alternation of the magnetic field and outputs counter pulses. By counting out the counter pulses the difference angle can be determined. Only through the marking of a start point, for example marked by several pulses with same polarity or by an additional sensor configuration, can the absolute rotational angle be determined. In alternative embodiments, such as for example introduced in DE 101 04 855 A1, the sequence of the counter pulses is utilized as additional information. However, in this case three sensors are required.
In comparison with the utilization of analog signals, the counting of counter pulses offers the advantage that the signal-to-noise ratio is significantly increased, which means interferences have a lesser effect on the quality of the signal analysis.
Apart from the known advantages of such steering arrangements, such as for example the low energy consumption or the capacity for good adaptation to the desired steering behavior of the motor vehicle, there is, however, a large number of new problems to be resolved.
In the first instance the response behavior and the precision of the wheel angle of the steering arrangement must be at least as good as in a conventional mechanical steering arrangement with hydraulic steering booster. Derived therefrom are several requirements made of the steering arrangement. First, the driver's desire, which means the desired wheel angle must be determined by the steering arrangement. The angle determination of the rotating components of the device with respect to the non-rotating components must take place with certainty and rapidly. Subsequently, from the measured values rapidly and with certainty the necessary power introduction into the electric power-assisted drive must be determined. Furthermore, the power assist or the electric drive, while circumventing the mechanical coupling, must be fed with minimum loss into the steering gearing. Lastly, the actually attained steering angle must be measured in order to close the positioning regulation circuit. Placed under the positioning regulation circuit, the regulation circuit for the power control of the electronically commutated electric motor must be closed.
However, the known systems have several distinct disadvantages. Thus, absolute values of the angles can only be acquired after passing through a relatively large angular range, for example, one complete rotation. Furthermore there is the risk of missing a marked starting point or a counter pulse, such that the angle measurement is erroneous. Moreover, a starting point must be defined. This leads either to a decrease of the resolution in the proximity of the starting point through the use of a longer pulse duration or to the need for a separate starting point detection sensor. In addition, most systems require several sensors, to some extent even more than 2 sensors, for acquiring the angular position.
The present invention addresses the problem of eliminating the disadvantages of prior art. The problem addressed comprises, for one, to bring into agreement the commutation of the current flow with the rotational position of the motor and, for another, to carry out the regulation very rapidly and smoothly so that no torsional fluctuations are introduced into the steering system, which are perceived by the driver as weaving or shimmy during the steering. This means that the angle of the rotor with respect to the stator of the electric motor must be acquired rapidly and with certainty. In addition the configuration must be reliably, simply and economically realizable.
The subject matter of the invention deals with the acquisition by sensory means of the rotor angle as a basis for the optimal regulation of the steering system, in particular of the electronic control of the electric motor.
The invention solves the problem of the sensory acquisition of the angles between the rotationally moved components with respect to the non-rotationally moved components through an arrangement according to the invention in simple manner and with comparatively low sensor expenditure. The dependent claims indicate further preferred embodiments. The invention includes the method for the solution of the problem.